High solids pcc with copolymeric additive

ABSTRACT

The present invention relates to a process for producing an aqueous suspension of precipitated calcium carbonate, an aqueous suspension of precipitated calcium carbonate and a precipitated calcium carbonate obtained by the process, a product comprising the aqueous suspension of precipitated calcium carbonate or the precipitated calcium carbonate as well as its use.

The present invention relates to a process for producing an aqueoussuspension of precipitated calcium carbonate, an aqueous suspension ofprecipitated calcium carbonate and a precipitated calcium carbonateobtained by the process, a product comprising the aqueous suspension ofprecipitated calcium carbonate or the precipitated calcium carbonate aswell as its use.

Calcium carbonate is one of the most commonly used additives in thepaper, paint and plastics industries. While naturally occurring groundcalcium carbonate (GCC) is usually used as a filler in manyapplications, synthetically manufactured precipitated calcium carbonate(PCC) may be tailor-made with respect to its morphology and particlesize allowing this materials to fulfil additional functions.

Commonly known PCC production processes including the steps of slakingquicklime with water, and subsequently precipitating calcium carbonateby passing carbon dioxide through the resulting calcium hydroxidesuspension, produce only PCC slurries with low solids content.Therefore, these processes typically comprise a subsequent solidsconcentration step in order to obtain a more concentrated PCC slurry,for example, for shipping the PCC slurry. However, such additionalsolids concentration steps are energy-consuming and cost-intensive andrequire equipment such as a centrifuge, which is expensive and needshigh maintenance. Furthermore, mechanical dewatering processes usingcentrifuges can destroy the structure of the formed PCC, for example, incase of clustered scalenohedral PCC.

WO 2011/121065 A1 discloses a process for preparing PCC comprising interalia the step of preparing an aqueous suspension of PCC seeds bycarbonating a suspension of calcium hydroxide in the presence ofstrontium hydroxide. A process for producing PCC, wherein the additionrate of the calcium carbonate slurry to the reaction vessel is such thata certain electrical conductivity is maintained in the reaction vessel,is described in EP 2 537 900 A1.

US 2011/158890 A1 describes a method to manufacture PCC involving theuse of a comb polymer, which reduces the carbonation time of the PCC. Agrinding agent for grinding coarse lime is disclosed in EP 0 313 483 A1.EP 2 447 213 A1 relates to the production of high purity PCC involvingthe step of slaking lime with an aqueous ammonium chloride solution.

WO 2013/142473 A1 relates to a process comprising the steps of slakingquick lime to obtain slaked lime, and subjecting the slaked lime,without agitation, without prior cooling in a heat exchanger, and in theabsence of any additives, to carbonation with carbon dioxide gas toproduce PCC. PCC production processes including additives are disclosedin U.S. Pat. Nos. 6,294,143, 5,232,678, and 5,558,850. A method forproducing slaked lime by slaking lime with a polymer having anionicgroups is described in JP 2008/074629 A. EP 0 844 213 A1 discloses amethod of producing a precipitate of an alkaline earth metal compoundinvolving the use of a dispersing agent.

WO 2010/018432 A1 discloses a process to prepare precipitated calciumcarbonate implementing low charge acrylate and/or maleinate-containingpolymers. A process for producing platy precipitated calcium carbonateinvolving the step of adding a polyacrylate to a suspension of calciumhydroxide prior to the completion of carbonation is described in WO2005/000742 A1. WO 2004/106236 A1 relates to a process for producingplaty precipitated calcium carbonate involving the step of adding a drycondensed phosphate additive to a suspension of calcium hydroxide priorto the completion of carbonation.

It is further known from applicants' unpublished application EP 14 166751.9 that an aqueous suspension of precipitated calcium carbonate canbe prepared by carbonating a milk of lime, which has been obtained bymixing water, a calcium oxide containing material, at least onewater-soluble polymer having a molecular weight M_(w) in the range from200 to 6 500 g/mol, and at least one slaking additive, wherein thecalcium oxide containing material and the water are mixed in a weightratio from 1:2.5 to 1:6. The at least one water-soluble polymer has thechemical structure of formula (I)

wherein n, m, and p are integers and at least one of n, m, or p isgreater than zero and n+m+p is less than or equal to 70,

R₁ is H or CH₃,

R₂ is H or CH₃;

R₃ is —C(═O)—O—R₄ or —C(═O)—NH—R₄, wherein R₄ is a C₁ to C₂₀ alkylgroup, a C₃ to C₂₀ cycloalkyl group and/or a C₆ to C₃₀ aryl group, beingoptionally substituted with one or more sulphonate groups, and whereinthe cycloalkyl group and/or the aryl group comprises one ring or severalrings, which are linked to each other, and

X is H and/or M, wherein M is Na, K, Li, Mg, and/or Ca, and wherein thestructural units

are arranged randomly, regularly and/or in blocks.

Furthermore, reference is made to the applicant's unpublishedapplication EP 15 157 025.6, which describes a process for producing anaqueous suspension of precipitated calcium carbonate, wherein a milk oflime is carbonated, which is obtained from mixing water, a calcium oxidecontaining material, and at least one cationic polymer.

Furthermore, reference is made to the applicant's unpublishedapplication EP 15 177 344.7, which describes a process for producing anaqueous suspension of precipitated calcium carbonate, wherein a milk oflime is carbonated, which is obtained from mixing water, a calcium oxidecontaining material, and at least one depolymerized carboxylatedcellulose having a molecular weight M_(w) in the range from 10 000 to 40000 g/mol.

A method for preparing calcium carbonate using additives andprecipitation agents is also known from KR100958593 B1. The methodcomprises an elution step of adding, into a container equipped with anagitator, a lime-based byproduct comprising steel-making slag or quicklime (CaO) dust, water at a ratio of 20 to 50 l per 60 to 100 g of thelime-based byproduct, at least one additive selected from the groupconsisting of sodium trimetaphosphate, sodium hexametaphosphate, sodiumpolycarbonate, ammonium polycarbonate, sodium polycarboxylate, formicacid, succinic acid, sucrose fatty acid ester, sodium citrate, ammoniumcitrate, and ammonium chloride in an amount of 0.01 to 10.0 parts byweight with respect to 100 parts by weight of the lime-based byproduct,and at least one precipitating agent selected from the group consistingof a cationic precipitating agent, an anionic precipitating agent, and anonionic precipitating agent in an amount of 0.01 to 3.0 parts by weightwith respect to 100 parts by weight of the lime-based byproduct andperforming a mixing, to elute calcium ions; a precipitation step ofstanding the resulting mixture for a predetermined period of time afterthe completion of mixing the lime-based byproduct, water, the additive,and the precipitating agent in the elution step to precipitate thelime-based byproduct; a carbonation step of separating a clearsupernatant eluate after the completion of the precipitation step andthen feeding carbon dioxide into the eluate to cause a reaction untilthe eluate is at pH 9; and a calcium carbonate collection step ofcollecting calcium carbonate precipitated on the bottom after thecompletion of the carbonation step.

However, said methods have the drawback that an additive in combinationwith a precipitating agent has to be added to the calcium oxidecomprising material. Furthermore, especially in KR100958593 B1, it isdescribed that the obtained mixture is separated in a precipitatedbottom portion and a clear supernatant eluate. The carbonating and theresulting precipitation of calcium carbonate is then only carried out onthe obtained clear supernatant eluate in order to obtain a calciumcarbonate product comprising less impurities. Thus, said method requiresadditional separation steps allowing a separation of solid and liquidphase during processing which results in a more time and cost-consumingproduction of precipitated calcium carbonate. Furthermore, it is to benoted that the precipitation agent is used in said method for adsorbingthe slurry suspended in water to coagulate and precipitate the slurrythrough cross-linking, which enables a rapid solid-liquid separation.However, due to the following separation of the liquid and solid phasesand carbonating of only the liquid phase, i.e. the clear supernatanteluate, the precipitation agent is not present in the carbonating stepand is thus not used for the following precipitation of calciumcarbonate.

WO 2007/067146 A1 is concerned with a method of producing precipitatedcalcium carbonate, wherein the carbonation of calcium hydroxide isperformed in the presence of starch or carboxymethylcellulose.

In view of the foregoing, there is a continuous need for processesproviding precipitated calcium carbonate, and especially those whichallow the direct production of PCC suspensions with a high solidscontent without an additional separation or concentration step.

Accordingly, it is an object of the present invention to provide aprocess for producing a PCC suspension with a high solids content at anacceptable viscosity. It is also desirable that said process does notrequire any mechanical or thermal concentration step during processing.It is also desirable that said process does not require any separationstep during processing, especially before the milk of lime iscarbonated. It is also desirable that said process does not affect thekinetics of the carbonation step in a negative way and/or does notimpair the crystallographic structure of the PCC.

The foregoing and other objects are solved by the subject-matter asdefined herein in the independent claims.

According to one aspect of the present invention, a process forproducing an aqueous suspension of precipitated calcium carbonate isprovided, the process comprising the steps of:

-   -   i) providing a calcium oxide containing material,    -   ii) providing at least one copolymer of the following formula        (I)

-   -   -   wherein x, y and z are present in blocks, alternating or            randomly; x is >0 and at least one of y or z is >0 and the            sum of x+y+z is ≤150; R₁ represents hydrogen or a sulphonic            functional group; R₂ represents a heteroatom, optionally            substituted with an alkyl group, an alkenyl group, an            heteroaryl group and/or a polyalkoxylated group; R₃ and R₄            are independently from each other a hydroxyl group, (O⁻M⁺)            with M⁺ being a monovalent, divalent or trivalent cation, an            O-alkyl group comprising from 1 to 20 carbon atoms, an            N-alkyl group comprising from 1 to 20 carbon atoms and/or a            polyalkoxylated group,

    -   iii) preparing a milk of lime by mixing water, the calcium oxide        containing material of step i), and the at least one copolymer        of step ii) to obtain a milk of lime, wherein the calcium oxide        containing material and the water are mixed in a weight ratio        from 1:1 to 1:12, and

    -   iv) carbonating the milk of lime obtained in step iii) to form        an aqueous suspension of precipitated calcium carbonate.

According to another aspect, the present invention provides an aqueoussuspension of precipitated calcium carbonate obtainable by the processaccording to the present invention.

According to a further aspect, the present invention provides a productcomprising an aqueous suspension of precipitated calcium carbonateaccording to the present invention, preferably the product is an aqueousformulation, and more preferably is a coating formulation, a papercoating formulation, a pharmaceutical formulation, an agriculturalformulation, a cosmetic formulation or an oral care formulation.

According to still another aspect, the present invention provides aprecipitated calcium carbonate obtainable by the process according tothe present invention.

According to a still further aspect, a product comprising precipitatedcalcium carbonate according to the present invention is provided,preferably the product is a paper, a paper product, an ink, a paint, acoating, a plastic, a polymer composition, an adhesive, a buildingproduct, a foodstuff, an agricultural product, a cosmetic product or apharmaceutical product, and more preferably the precipitated calciumcarbonate is a dried precipitated calcium carbonate and the product is aplastic or a polymer composition.

According to still another aspect, a use of the aqueous suspension ofprecipitated calcium carbonate according to the present invention and/orprecipitated calcium carbonate according to the present invention inpaper, plastics, polymer compositions, paint, coatings, concrete,cosmetics, pharmaceutics and/or agriculture applications is provided,wherein preferably a dried precipitated calcium carbonate, morepreferably a dried powder of precipitated calcium carbonate, is used inplastics and/or polymer compositions.

Advantageous embodiments of the present invention are defined in thecorresponding sub-claims.

According to one embodiment, step iii) comprises the steps of: a1)mixing the at least one copolymer of step ii) with water, and a2) addingthe calcium oxide containing material of step i) to the mixture of stepa1); or b1) mixing the calcium oxide containing material of step i), andthe at least one copolymer of step ii), and b2) adding water to themixture of step b1); or c) mixing the calcium oxide containing materialof step i), the at least one copolymer of step ii) and watersimultaneously.

According to another embodiment, the process further comprises step v)of adding at least one slaking additive to process step iii), preferablythe at least one slaking additive is selected from the group consistingof organic acids, organic acid salts, sugar alcohols, monosaccharides,disaccharides, polysaccharides, gluconates, phosphonates,lignosulphonates, and mixtures thereof.

According to yet another embodiment, the milk of lime obtained in stepiii) has a Brookfield viscosity from 1 to 1 000 mPa·s at 25° C., morepreferably from 5 to 800 mPa·s at 25° C., and most preferably from 10 to500 mPa·s at 25° C.; and/or the suspension of PCC obtained in step iv)has a Brookfield viscosity of less than or equal to 3 000 mPa·s at 25°C., more preferably less than or equal to 2 500 mPa·s at 25° C., andmost preferably less than or equal to 600 mPa·s at 25° C.

According to one embodiment, the suspension of PCC obtained in step iv)has solids content of at least 15 wt.-%, preferably from 15 to 70 wt.-%,more preferably from 19 to 60 wt.-%, even more preferably from 21 to 50wt.-% and most preferably from 24 to 42 wt.-%, based on the total weightof the suspension.

According to another embodiment, the temperature of the water, which isused in mixing step iii), is adjusted to be in the range from more than0° C. and less than 100° C., preferably from 1° C. to 85° C., morepreferably from 2° C. to 70° C., even more preferably from 30° C. to 65°C., and most preferably from 35 to 55° C.; and/or the temperature of themilk of lime obtained in step iii), which is employed in step iv), isadjusted to be in the range from 20° C. to 65° C., and preferably from30° C. to 55° C.

According to yet another embodiment, the at least one copolymer of stepii) is a compound of the following formula (II)

-   -   wherein x and y are present in blocks, alternating or randomly;        x and y are >0 and the sum of x+y is ≤150; R₁ represents        hydrogen or a sulphonic functional group; R₂ represents a        heteroatom, optionally substituted with an alkyl group, an        alkenyl group, an heteroaryl group and/or a polyalkoxylated        group.

According to one embodiment, the at least one copolymer of step ii) is acompound of the following formula (III)

-   -   wherein x and z are present in blocks, alternating or randomly;        x and z are >0 and the sum of x+z is ≤150; R₁ represents        hydrogen or a sulphonic functional group; R₃ is a hydroxyl        group, (O⁻M⁺) with M⁺ being a monovalent, divalent or trivalent        cation, an O-alkyl group comprising from 1 to 20 carbon atoms,        an N-alkyl group comprising from 1 to 20 carbon atoms and/or a        polyalkoxylated group; and M⁺ being a monovalent, divalent or        trivalent cation.

According to another embodiment, the molar ratio of x to y and/or z inthe at least one copolymer of step ii) [x:y and/or z] is from 10:1 to1:2, preferably from 5:1 to 1:2 and most preferably about 1:1, 2:1 or3:1.

According to yet another embodiment, the at least one copolymer of stepii) has a molecular weight M_(w) in the range from 500 to 100 000 g/mol,preferably from 1 000 to 50 000 g/mol, more preferably from 2 000 to 20000 g/mol and most preferably from 2 500 to 10 000 g/mol; and/or,provided in a water solution, has a Brookfield viscosity of less than orequal to 5 000 mPa·s at 25° C., more preferably less than or equal to 2000 mPa·s at 25° C., and most preferably less than or equal to 1 500mPa·s at 25° C.

According to one embodiment, the process further comprises step vi) ofseparating the precipitated calcium carbonate from the aqueoussuspension obtained in step iv), and optionally step vii) of drying theseparated precipitated calcium carbonate obtained in step vi).

According to another embodiment the process further comprises step vi)of separating the precipitated calcium carbonate from the aqueoussuspension obtained in step iv), and optionally step vii) of drying theseparated precipitated calcium carbonate obtained in step vi).

According to yet another embodiment, the process further comprises astep viii) of contacting at least a part of the surface of the obtainedprecipitated calcium carbonate with at least one hydrophobising agentafter step iv) and/or after step vi), if present, and/or during and/orafter step vii), if present, preferably the at least one hydrophobisingagent is selected from the group consisting of an aliphatic carboxylicacid having a total amount of carbon atoms from C₄ to C₂₄ and/orreaction products thereof, a mono-substituted succinic anhydrideconsisting of succinic anhydride mono-substituted with a group selectedfrom a linear, branched, aliphatic and cyclic group having a totalamount of carbon atoms from at least C₂ to C₃₀ in the substituent and/orreaction products thereof, a phosphoric acid ester blend of one or morephosphoric acid mono-ester and/or reaction products thereof and one ormore phosphoric acid di-ester and/or reaction products thereof,polyhydrogensiloxane and reaction products thereof, an inert siliconeoil, preferably polydimethylsiloxane, an aliphatic aldehyde having from6 to 14 carbon atoms and/or reaction products thereof, and mixturesthereof.

It should be understood that for the purpose of the present invention,the following terms have the following meaning:

A “calcium oxide containing material” in the meaning of the presentinvention can be a mineral or a synthetic material having a content ofcalcium oxide of at least 50 wt.-%, preferably 75 wt.-%, more preferably90 wt.-%, and most preferably 95 wt.-%, based on the total weight of thecalcium oxide containing material. For the purpose of the presentinvention, a “mineral material” is a solid substance having a definiteinorganic chemical composition and characteristic crystalline and/oramorphous structure.

“Ground calcium carbonate” (GCC) in the meaning of the present inventionis a calcium carbonate obtained from natural sources, such as limestone,marble, or chalk, and processed through a wet and/or dry treatment suchas grinding, screening and/or fractionation, for example by a cyclone orclassifier.

Throughout the present document, the “particle size” of precipitatedcalcium carbonate or other particulate materials is described by itsdistribution of particle sizes. The value d_(x) represents the diameterrelative to which x % by weight of the particles have diameters lessthan d_(x). This means that the d₂₀ value is the particle size at which20 wt.-% of all particles are smaller, and the d₉₈ value is the particlesize at which 98 wt.-% of all particles are smaller. The d₉₈ value isalso designated as “top cut”. The d₅₀ value is thus the weight medianparticle size, i.e. 50 wt.-% of all grains are smaller than thisparticle size. For the purpose of the present invention the particlesize is specified as weight median particle size d₅₀ unless indicatedotherwise. For determining the weight median particle size d₅₀ value orthe top cut particle size d₉₈ value a Sedigraph 5100 or 5120 device fromthe company Micromeritics, USA, can be used.

“Precipitated calcium carbonate” (PCC) in the meaning of the presentinvention is a synthesized material, generally obtained by precipitationfollowing a reaction of carbon dioxide and calcium hydroxide (hydratedlime) in an aqueous environment or by precipitation of a calcium- and acarbonate source in water. Additionally, precipitated calcium carbonatecan also be the product of introducing calcium and carbonate salts,calcium chloride and sodium carbonate for example, in an aqueousenvironment. PCC may have a vateritic, calcitic or aragoniticcrystalline form. PCCs are described, for example, in EP 2 447 213 A1,EP 2 524 898 A1, EP 2 371 766 A1, or WO 2013/142473 A1.

A “suspension” or “slurry” in the meaning of the present inventioncomprises insoluble solids and water, and optionally further additives,and usually contains large amounts of solids and, thus, is more viscousand can be of higher density than the liquid from which it is formed.

For the purpose of the present invention, the “solids content” of aliquid composition such as a suspension or slurry is a measure of theamount of material remaining after all the solvent or water has beenevaporated.

A “copolymer” in the meaning of the present invention is a polymer thathas been prepared by polymerizing two or more different monomerstogether. The two or more different monomers of the copolymer of thepresent invention can be present in blocks, alternating or randomly.

A “specific BET surface area” (SSA) in the meaning of the presentinvention is defined as the surface area of the precipitated calciumcarbonate particles divided by the mass of PCC particles. As usedtherein the specific surface area is measured by adsorption using theBET isotherm (ISO 9277:1995) and is specified in m²/g.

For the purpose of the present invention, the term “viscosity” or“Brookfield viscosity” refers to Brookfield viscosity. The Brookfieldviscosity is for this purpose measured by a Brookfield DV-II+ Proviscometer at 25° C.±1° C. at 100 rpm using an appropriate spindle ofthe Brookfield RV-spindle set and is specified in mPa·s. Based on histechnical knowledge, the skilled person will select a spindle from theBrookfield RV-spindle set which is suitable for the viscosity range tobe measured. For example, for a viscosity range between 200 and 800mPa·s the spindle number 3 may be used, for a viscosity range between400 and 1 600 mPa·s the spindle number 4 may be used, for a viscosityrange between 800 and 3 200 mPa·s the spindle number 5 may be used, fora viscosity range between 1 000 and 2 000 000 mPa·s the spindle number 6may be used, and for a viscosity range between 4 000 and 8 000 000 mPa·sthe spindle number 7 may be used.

Unless specified otherwise, the term “drying” refers to a processaccording to which at least a portion of water is removed from amaterial to be dried such that a constant weight of the obtained “dried”material at 120° C. is reached. Moreover, a “dried” material may befurther defined by its total moisture content which, unless specifiedotherwise, is less than or equal to 1.0 wt.-%, preferably less than orequal to 0.5 wt.-%, more preferably less than or equal to 0.2 wt.-%, andmost preferably between 0.03 and 0.07 wt.-%, based on the total weightof the dried material.

The “total moisture content” of a material refers to the percentage ofmoisture (i.e. water) which may be desorbed from a sample upon heatingto 220° C.

In the meaning of the present invention, “stable in an aqueoussuspension having a pH of 12 and a temperature of 95° C.” means that thecopolymer maintains its physical properties and chemical structure whenadded to an aqueous suspension having a pH of 12 and a temperature of95° C. For example, the copolymer maintains its dispersing qualities andis not degraded under said conditions.

Where the term “comprising” is used in the present description andclaims, it does not exclude other non-specified elements of major orminor functional importance. For the purposes of the present invention,the term “consisting of” is considered to be a preferred embodiment ofthe term “comprising of”. If hereinafter a group is defined to compriseat least a certain number of embodiments, this is also to be understoodto disclose a group, which preferably consists only of theseembodiments.

Whenever the terms “including” or “having” are used, these terms aremeant to be equivalent to “comprising” as defined above.

Where an indefinite or definite article is used when referring to asingular noun, e.g. “a”, “an” or “the”, this includes a plural of thatnoun unless something else is specifically stated.

Terms like “obtainable” or “definable” and “obtained” or “defined” areused interchangeably. This e.g. means that, unless the context clearlydictates otherwise, the term “obtained” does not mean to indicate thate.g. an embodiment must be obtained by e.g. the sequence of stepsfollowing the term “obtained” even though such a limited understandingis always included by the terms “obtained” or “defined” as a preferredembodiment.

The inventive process for producing an aqueous suspension ofprecipitated calcium carbonate comprising the steps of i) providing acalcium oxide containing material, ii) providing at least one copolymerof the following formula (I)

-   -   wherein x, y and z are present in blocks, alternating or        randomly; x is >0 and at least one of y or z is >0 and the sum        of x+y+z is ≤150; R₁ represents hydrogen or a sulphonic        functional group; R₂ represents a heteroatom, optionally        substituted with an alkyl group, an alkenyl group, an heteroaryl        group and/or a polyalkoxylated group; R₃ and R₄ are        independently from each other a hydroxyl group, (O⁻M⁺) with M⁺        being a monovalent, divalent or trivalent cation, an O-alkyl        group comprising from 1 to 20 carbon atoms, an N-alkyl group        comprising from 1 to 20 carbon atoms and/or a polyalkoxylated        group; iii) preparing a milk of lime by mixing water, the        calcium oxide containing material of step i), and the at least        one copolymer of step ii) to obtain a milk of lime, wherein the        calcium oxide containing material and the water are mixed in a        weight ratio from 1:1 to 1:12, and iv) carbonating the milk of        lime obtained in step iii) to form an aqueous suspension of        precipitated calcium carbonate.

In the following details and preferred embodiments of the inventiveprocess will be set out in more details. It is to be understood thatthese technical details and embodiments also apply to the inventiveproducts as well as to their use.

Process Step i): Provision of a Calcium Oxide Containing Material

According to step i) of the process of the present invention, a calciumoxide containing material is provided.

The calcium oxide containing material of step i) can be obtained bycalcining a calcium carbonate containing material. Calcination is athermal treatment process applied to calcium carbonate containingmaterials in order to bring about a thermal decomposition resulting inthe formation of calcium oxide and gaseous carbon dioxide. Calciumcarbonate containing materials which may be used in such a calcinationsprocess are those selected from the group comprising precipitatedcalcium carbonates, natural calcium carbonate containing minerals suchas marble, limestone and chalk, and mixed alkaline earth carbonateminerals comprising calcium carbonate such as dolomite, or calciumcarbonate rich fractions from other sources. It is also possible tosubject a calcium carbonate containing waste material to a calcinationsprocess in order to obtain a calcium oxide containing material. Calciumcarbonate decomposes at about 1 000° C. to calcium oxide (commonly knownas quicklime). The calcination step may be carried out under conditionsand using equipment well-known to the person skilled in the art.Generally, calcination may be carried out in furnaces or reactors(sometimes referred to as kilns) of various designs including shaftfurnaces, rotary kilns, multiple hearth furnaces, and fluidized bedreactors.

The end of the calcination reaction may be determined, e.g. bymonitoring the density change, the residual carbonate content, e.g. byX-ray diffraction, or the slaking reactivity by common methods.

According to one embodiment of the present invention, the calcium oxidecontaining material of step i) is obtained by calcining a calciumcarbonate containing material, preferably selected from the groupconsisting of precipitated calcium carbonate, natural calcium carbonateminerals such as marble, limestone and chalk, mixed alkaline earthcarbonate minerals comprising calcium carbonate such as dolomite, andmixtures thereof.

For reasons of efficiency, it is preferred that the calcium oxidecontaining material has a minimum calcium oxide content of at least 75wt.-%, preferably at least 90 wt.-%, and most preferably 95 wt.-%, basedon the total weight of the calcium oxide containing material. Accordingto one embodiment, the calcium oxide containing material consists ofcalcium oxide.

The calcium oxide containing material can consist of only one type ofcalcium oxide containing material. Alternatively, the calcium oxidecontaining material can consist of a mixture of two or more types ofcalcium oxide containing materials.

The calcium oxide containing material can be used in the inventiveprocess in its original form, i.e. as a raw material, for example, inform of smaller and bigger chunks. Alternatively, the calcium oxidecontaining material can be ground before use. According to oneembodiment of the present invention, the calcium carbonate containingmaterial is in forms of particles having weight median particle size d₅₀from 0.1 to 1 000 μm, and preferably from 1 to 500 μm.

Process Step ii): Provision of at Least One Copolymer

According to step ii) of the process of the present invention, at leastone copolymer is provided.

The term “at least one” copolymer in the meaning of the presentinvention means that the copolymer comprises, preferably consists of,one or more copolymer(s).

In one embodiment of the present invention, the at least one copolymercomprises, preferably consists of, one copolymer. Alternatively, the atleast one copolymer comprises, preferably consists of, two or morecopolymers. For example, the at least one copolymer comprises,preferably consists of, two copolymers.

Preferably, the at least one copolymer comprises, more preferablyconsists of, one copolymer.

It is one requirement of the present invention that the at least onecopolymer is of the following formula (I)

wherein x, y and z are present in blocks, alternating or randomly; xis >0 and at least one of y or z is >0 and the sum of x+y+z is ≤150; R₁represents hydrogen or a sulphonic functional group; R₂ represents aheteroatom, optionally substituted with an alkyl group, an alkenylgroup, an heteroaryl group and/or a polyalkoxylated group; R₃ and R₄ areindependently from each other a hydroxyl group, (O⁻M⁺) with M⁺ being amonovalent, divalent or trivalent cation, an O-alkyl group comprisingfrom 1 to 20 carbon atoms, an N-alkyl group comprising from 1 to 20carbon atoms and/or a polyalkoxylated group.

As used herein, the term “alkyl” is a radical of a saturated aliphaticgroup, including linear chain alkyl groups, branched chain alkyl groupsand cyclic chain alkyl groups comprising from 1 to 20 carbon atoms,wherein such linear, branched and cyclic chain alkyl groups may each beoptionally substituted, e.g. with a hydroxyl group.

As used herein, the term “alkenyl” is a radical of an unsaturatedaliphatic group, including linear chain alkenyl groups, branched chainalkenyl groups and cyclic chain alkenyl groups comprising from 2 to 20carbon atoms, wherein such linear, branched and cyclic chain alkenylgroups may each be optionally substituted, e.g. with a hydroxyl group.The alkenyl group can feature one or more insaturations.

As used herein, the term “heteroatom” refers to an oxygen, sulphur ornitrogen atom, preferably an oxygen atom.

As used herein, the “sulphonic” functional group refers to a —SO₃H or(SO₃ ⁻, M⁺).

The term “polyalkoxylated group” in the meaning of the present inventionrefers to the group [(EO)_(n)(PO)_(n′)(BO)_(n″)]—Z. The alkoxylatedunits are present in blocks, alternating or randomly, and are selectedfrom ethoxylated units EO, propoxylated units PO and butoxylated unitsBO. n, n′, n″ are independently from each other each 0 or an integer inthe range from 1 to 150, the sum of n, n′ and n″ is >0 and Z is an alkylgroup comprising from 1 to 20 carbon atoms, e.g. 1 or 2 carbon atoms.

In one embodiment, R₂ is a nitrogen atom being substituted with an alkylgroup, an alkenyl group, an heteroaryl group and/or a polyalkoxylatedgroup. For example, the nitrogen atom can be substituted with an alkylgroup comprising a primary ammonium, secondary ammonium or tertiaryammonium function. Preferably, R₂ is N—CH₂—CH₂—N(CH₃)₂.

In the at least one copolymer of the formula (I), x, y and z can bepresent in blocks, alternating or randomly. Preferably, x, y and z arepresent alternating or randomly in the at least one copolymer of theformula (I). More preferably, x, y and z are present alternating in theat least one copolymer of the formula (I).

It is appreciated that x is >0 and at least one of y or z is >0 and thesum of x+y+z is ≤150 in the at least one copolymer of the formula (I).

In one embodiment, x, y and z are >0 and the sum of x+y+z is ≤150 in theat least one copolymer of the formula (I). For example, x, y and z areindependently from each other each an integer in the range from 1 to 148and the sum of x+y+z is an integer in the range from 3 to 150 in the atleast one copolymer of the formula (I).

Thus, the at least one copolymer can be a compound of the formula (I),wherein x, y and z are present alternating or randomly; x, y and zare >0 and the sum of x+y+z is ≤150; R₁ represents hydrogen; R₂represents a heteroatom, optionally substituted with an alkyl group; R₃and R₄ are independently from each other a hydroxyl group, (O⁻M⁺) withM⁺ being a monovalent, divalent or trivalent cation, or an O-alkyl groupcomprising from 1 to 20 carbon atoms.

For example, the at least one copolymer can be a compound of the formula(I), wherein x, y and z are present alternating; x, y and z areindependently from each other an integer in the range from 1 to 148 andthe sum of x+y+z is an integer in the range from 3 to 150; R₁ representshydrogen; R₂ represents a heteroatom; R₃ and R₄ are independently fromeach other a (O⁻M⁺) with M⁺ being a monovalent, divalent or trivalentcation.

Preferably, the at least one copolymer can be a compound of the formula(I), wherein x, y and z are present alternating; x, y and z areindependently from each other an integer in the range from 1 to 148 andthe sum of x+y+z is an integer in the range from 3 to 150; R₁ representshydrogen; R₂ represents a heteroatom such as oxygen; R₃ and R₄ areindependently from each other a (O⁻M⁺) with M⁺ being a monovalent cationsuch as sodium.

In another embodiment, it is preferred that x is >0 and y or z is 0.

For example, x and y are >0 and z is 0 and the sum of x+y+z is ≤150 inthe at least one copolymer of the formula (I). For example, x and y areindependently from each other each an integer in the range from 1 to 149and z is 0 and the sum of x+y+z is an integer in the range from 2 to 150in the at least one copolymer of the formula (I).

Alternatively, x and z are >0 and y is 0 and the sum of x+y+z is ≤150 inthe at least one copolymer of the formula (I). For example, x and z areindependently from each other each an integer in the range from 1 to 149and y is 0 and the sum of x+y+z is an integer in the range from 2 to 150in the at least one copolymer of the formula (I).

Thus, the at least one copolymer is preferably a compound of thefollowing formula (II)

wherein x and y are present in blocks, alternating or randomly; x and yare >0 and the sum of x+y is ≤150; R₁ represents hydrogen or a sulphonicfunctional group; R₂ represents a heteroatom, optionally substitutedwith an alkyl group, an alkenyl group, an heteroaryl group and/or apolyalkoxylated group.

For example, the at least one copolymer is a compound of the formula(II), wherein x and y are present alternating or randomly; x and y areindependently from each other each an integer in the range from 1 to 149and the sum of x+y is an integer in the range from 2 to 150; R₁represents hydrogen or a sulphonic functional group; R₂ represents aheteroatom, optionally substituted with an alkyl group, an alkenylgroup, an heteroaryl group and/or a polyalkoxylated group.

Preferably, the at least one copolymer is a compound of the formula(II), wherein x and y are present alternating or randomly; x and y areindependently from each other each an integer in the range from 1 to 149and the sum of x+y is an integer in the range from 2 to 150; R₁represents hydrogen; R₂ represents a heteroatom, optionally substitutedwith an alkyl group.

More preferably, the at least one copolymer is a compound of the formula(II), wherein x and y are present alternating; x and y are independentlyfrom each other each an integer in the range from 1 to 149 and the sumof x+y is an integer in the range from 2 to 150; R₁ represents hydrogen;R₂ represents a heteroatom such as oxygen.

Alternatively, the at least one copolymer is a compound of the followingformula (III)

wherein x and z are present in blocks, alternating or randomly; x and zare >0 and the sum of x+z is ≤150; R₁ represents hydrogen or a sulphonicfunctional group; R₃ is a hydroxyl group, (O⁻M⁺) with M⁺ being amonovalent, divalent or trivalent cation, an O-alkyl group comprisingfrom 1 to 20 carbon atoms, an N-alkyl group comprising from 1 to 20carbon atoms and/or a polyalkoxylated group; and M⁺ being a monovalent,divalent or trivalent cation.

For example, the at least one copolymer is a compound of the formula(III), wherein x and z are present alternating or randomly; x and z areindependently from each other each an integer in the range from 1 to 149and the sum of x+z is an integer in the range from 2 to 150; R₁represents hydrogen; R₃ is (O⁻M⁺) with M⁺ being a monovalent cation, anO-alkyl group comprising from 1 to 20 carbon atoms and/or apolyalkoxylated group; and M⁺ being a monovalent cation.

Preferably, the at least one copolymer is a compound of the formula(III), wherein x and z are present alternating or randomly; x and z areindependently from each other each an integer in the range from 1 to 149and the sum of x+z is an integer in the range from 2 to 150; R₁represents hydrogen; R₃ is (O⁻M⁺) with M⁺ being a monovalent cation oran O-alkyl group comprising from 1 to 20 carbon atoms; and M⁺ being amonovalent cation.

More preferably, the at least one copolymer is a compound of the formula(III), wherein x and z are present alternating; x and z areindependently from each other each an integer in the range from 1 to 149and the sum of x+z is an integer in the range from 2 to 150; R₁represents hydrogen; R₃ is (O⁻M⁺) with M⁺ being a monovalent cation; andM⁺ being a monovalent cation.

In one embodiment, the at least one copolymer is a compound of theformula (III), wherein x and z are present randomly; x and z areindependently from each other each an integer in the range from 1 to 149and the sum of x+z is an integer in the range from 2 to 150; R₁represents hydrogen; R₃ is (O⁻M⁺) with M⁺ being a monovalent cation; andM⁺ being a monovalent cation, and M⁺ of (O⁻M⁺) and M⁺ being the samemonovalent cation.

It is appreciated that the copolymer of step ii) can be partially orcompletely neutralized.

As regards the term “monovalent cation”, it is appreciated that thisterm refers to a cation having a valency of one. Accordingly, the term“divalent cation” refers to a cation having a valency of two and theterm “trivalent cation” refers to a cation having a valency of three.

The monovalent cation is preferably selected from lithium, sodium,potassium and/or ammonium. More preferably, the monovalent cation isselected from lithium, sodium and/or potassium. Most preferably themonovalent cation is sodium and/or potassium. For example, themonovalent cation is sodium.

If the monovalent cation is ammonium, the at least one copolymer of stepii) is preferably partially neutralized. If the monovalent cation islithium, sodium or potassium, preferably sodium, the at least onecopolymer of step ii) is preferably completely neutralized.

In view of this, the at least one copolymer is preferably a compound ofthe formula (III), wherein x and z are present alternating; x and z areindependently from each other each an integer in the range from 1 to 149and the sum of x+z is an integer in the range from 2 to 150; R₁represents hydrogen; R₃ is (O⁻M⁺) with M⁺ being sodium or ammonium,preferably sodium; and M⁺ being sodium or ammonium, preferably sodium.

The divalent cation is preferably selected from calcium and/ormagnesium. More preferably, the divalent cation is calcium.

In this embodiment, the at least one copolymer is preferably a compoundof the formula (III), wherein x and z are present alternating; x and zare independently from each other each an integer in the range from 1 to149 and the sum of x+z is an integer in the range from 2 to 150; R₁represents hydrogen; R₃ is (O⁻M⁺) with M⁺ being calcium; and M⁺ beingcalcium.

The trivalent cation is preferably selected from Al³⁺ and/or Fe³⁺.

It is appreciated that the at least one copolymer of step ii) ispreferably obtained by polymerizing monomers selected from low molecularweight styrene and maleic anhydride. For example, the at least onecopolymer of step ii) is a low molecular weight copolymer comprising,preferably consisting of, styrene and maleic anhydride, and/orderivatives thereof.

In one embodiment, the copolymer derivative, preferably the derivativeof a copolymer comprising, preferably consisting of, styrene and maleicanhydride, comprises, preferably consists of:

-   -   units of maleic anhydride being partially or completely        hydrolyzed, and/or    -   units of maleic anhydride being partially or completely        esterified, and/or    -   units of maleic anhydride being partially or completely        amidified, and/or    -   units of maleic anhydride being partially or completely        imidized, and/or    -   units of styrene being partially or completely sulfonized.

In order to obtain a PCC suspension with a high solids content at anacceptable viscosity, it is especially preferred that themonomers/comonomers of the at least one copolymer of step ii) arepresent in a specific molar ratio.

In one embodiment, the molar ratio of x to y and/or z in the at leastone copolymer of step ii) [x:y and/or z] is from 10:1 to 1:2, preferablyfrom 5:1 to 1:2 and most preferably about 1:1, 2:1 or 3:1.

Preferably, the molar ratio of x to y and z in the at least onecopolymer of step ii) [x:y and z] is from 10:1 to 1:2, preferably from5:1 to 1:2 and most preferably about 1:1, 2:1 or 3:1. Alternatively, themolar ratio of x to y or z in the at least one copolymer of step ii)[x:y or z] is from 10:1 to 1:2, preferably from 5:1 to 1:2 and mostpreferably about 1:1, 2:1 or 3:1. For example, the molar ratio of x to zin the at least one copolymer of step ii) [x: z] is from 10:1 to 1:2,preferably from 5:1 to 1:2 and most preferably about 1:1, 2:1 or 3:1.This embodiment especially applies, in case the at least one copolymerof step ii) is a compound of the formula (III).

According to one embodiment of the present invention, the at least onecopolymer of step ii) has a molecular weight M_(w) in the range from 500to 100 000 g/mol, preferably from 1 000 to 50 000 g/mol, more preferablyfrom 2 000 to 20 000 g/mol and most preferably from 2 500 to 10 000g/mol. The molecular weight M_(w) may be determined by gel permeationchromatography.

Additionally or alternatively, the at least one copolymer of step ii),provided in a water solution, has a Brookfield viscosity of less than orequal to 5 000 mPa·s at 25° C., more preferably less than or equal to 2000 mPa·s at 25° C., and most preferably less than or equal to 1 500mPa·s at 25° C. Preferably, the at least one copolymer of step ii),provided in a water solution, has a Brookfield viscosity of less than orequal to 5 000 mPa·s at 25° C., more preferably less than or equal to 2000 mPa·s at 25° C., and most preferably less than or equal to 1 500mPa·s at 25° C., at copolymer content of 20 to 40 wt.-%, based on thetotal weight of the copolymer solution.

More preferably, the at least one copolymer of step ii), provided in awater solution, has a Brookfield viscosity of less than or equal to 1000 mPa·s at 25° C., and most preferably in the range from 100 to 1 000mPa·s at 25° C. Preferably, the at least one copolymer of step ii),provided in a water solution, has a Brookfield viscosity of less than orequal to 1 000 mPa·s at 25° C., and most preferably in the range from100 to 1 000 mPa·s at 25° C., at copolymer content of 20 to 40 wt.-%,based on the total weight of the copolymer solution.

According to one embodiment of the present invention, the at least onecopolymer of step ii) is added in an amount from 0.001 to 5 wt.-%,preferably from 0.01 to 2 wt.-%, more preferably from 0.05 to 1 wt.-%,and most preferably from 0.1 to 0.5 wt.-%, based on the total weight ofthe calcium oxide containing material in the milk of lime.

The at least one copolymer of step ii) can be provided in form of asolution or as a dry material. According to one embodiment, the at leastone copolymer of step ii) is provided in form of a solution. Accordingto another embodiment of the present invention, the at least onecopolymer of step ii) is provided in form of an aqueous solution havinga polymer concentration from 1 to 70 wt.-%, and preferably from 2 to 60wt.-%, based on the total weight of the aqueous solution.

According to the present invention, the at least one copolymer is addedduring step iii) of the inventive process for producing PCC, i.e. thecopolymer is added during the slaking step. As known to the skilledperson, the milk of lime obtained by slaking a calcium oxide containingmaterial with water has usually a pH value between 11 and 12.5 at atemperature of 25° C., depending on the concentration of the calciumoxide containing material in the milk of lime. Since the slakingreaction is exothermic, the temperature of the milk of lime typicallyraises to a temperature between 80 and 99° C. According to oneembodiment of the present invention, the at least one copolymer of stepii) is selected such that it is stable in an aqueous suspension having apH of 12 and a temperature of 95° C. In the meaning of the presentinvention, “stable in an aqueous suspension having a pH of 12 and atemperature of 95° C.” means that the copolymer maintains its physicalproperties and chemical structure when added to an aqueous suspensionhaving a pH of 12 and a temperature of 95° C. For example, the copolymermaintains its dispersing qualities and is not degraded under saidconditions.

Process Step iii): Preparing of the Milk of Lime

According to step iii) of the process of the present invention, a milkof lime is prepared by mixing water, the calcium oxide containingmaterial of step i), and the at least one copolymer of step ii) toobtain a milk of lime, wherein the calcium oxide containing material andthe water are mixed in a weight ratio from 1:1 to 1:12.

The reaction of the calcium oxide containing material with water resultsin the formation of a milky calcium hydroxide suspension, better knownas milk of lime. Said reaction is highly exothermic and is alsodesignated as “lime slaking” in the art.

According to one embodiment of the present invention, the temperature ofthe water, which is used in mixing step iii), i.e. the temperature ofthe water that is used to slake the calcium oxide containing material,is adjusted to be in the range from more than 0° C. and less than 100°C. In other words, the water that is used to slake the calcium oxidecontaining material is adjusted to a temperature range, in which thewater is in liquid form. Preferably, the temperature of the water, whichis employed in mixing step iii) is adjusted to be from 1° C. to 85° C.,more preferably from 2° C. to 70° C., even more preferably from 30° C.to 65° C., and most preferably from 35 to 55° C. It will be apparent tothe skilled person that the initial temperature of the water is notnecessarily the same one as the temperature of the mixture prepared instep iii) due to the highly exothermic slaking reaction and/or due tothe mixing of substances having different temperatures.

According to one embodiment of the present invention, process step iii)comprises the steps of:

-   -   a1) mixing the at least one copolymer of step ii) with water,        and    -   a2) adding the calcium oxide containing material of step i) to        the mixture of step a1).

According to one embodiment, step a1) is carried out at a temperaturefrom more than 0° C. to 99° C., preferably from 1° C. to 75° C., morepreferably from 2° C. to 70° C., even more preferably from 30° C. to 65°C., and most preferably from 35 to 55° C.

According to another embodiment of the present invention, process stepiii) comprises the steps of:

-   -   b1) mixing the calcium oxide containing material of step i), and        the at least one copolymer of step ii), and    -   b2) adding water to the mixture of step b1).

According to still another embodiment of the present invention, inprocess step iii) the calcium oxide containing material of step i), theat least one copolymer of step ii), and water are mixed simultaneously.

The at least one copolymer of step ii) may be added in step iii) in oneportion or in several portions. According to one embodiment, in stepiii) the at least one copolymer of step ii) is mixed with the water, andthe calcium oxide containing material of step i), by adding the at leastone copolymer in one portion or in two, three, four, five, or moreportions.

Process step iii) may be performed at room temperature, i.e. at atemperature of 20° C.±2° C., or at an initial temperature of 30 to 500,preferably 35 to 45° C. Since the reaction is exothermic, thetemperature typically raises to a temperature between 85 and 99° C.during step iii), preferably to a temperature between 90 and 95° C.According to a preferred embodiment, process step iii) is performedunder mixing, agitation, or stirring, for example, mechanical stirring.Suitable process equipment for mixing, agitation or stirring is known tothe skilled person.

The progress of the slaking reaction may be observed by measuring thetemperature and/or conductivity of the reaction mixture. It can also bemonitored by turbidity control. Alternatively or additionally, theprogress of the slaking reaction can be inspected visually.

Conventional methods for preparing PCC suffer from the problem that themilk of lime can only be processed at low solids content since the milkof lime becomes very viscous at higher solids content during the slakingprocess. In a typical PCC production process of the prior art, theweight ratio of calcium oxide to water is less than 1:6, usually 1:9 or1:10. The inventors surprisingly found that the addition of a copolymeras defined above, before or during the slaking step of a process forproducing PCC can allow the preparation of a milk of lime with a highsolids content. By carbonating said highly concentrated milk of lime, anaqueous suspension of PCC can be obtained which has also a high solidscontent. As a result, the process of the present invention does notrequire an additional concentration step in order to obtain a PCCsuspension with high solids content.

According to the present invention, the calcium oxide containingmaterial and the water are mixed in a weight ratio from 1:1 to 1:12.According to one preferred embodiment, in step iii) the calcium oxidecontaining material and the water are mixed in a weight ratio from 1:1to 1:9, more preferably from 1:2.5 to 1:5.

According to one embodiment of the present invention, the milk of limeof step iii) has a solids content of at least 8 wt.-%, preferably from10 to 66 wt.-%, more preferably from 12 to 66 wt.-%, even morepreferably from 15 to 55 wt.-%, and most preferably from 17 to 45 wt.-%,such as from 20 to 38 wt.-%, based on the total weight of the milk oflime.

According to one embodiment of the present invention, the milk of limeobtained in step iii) has a Brookfield viscosity from 1 to 1 000 mPa·sat 25° C., more preferably from 5 and 800 mPa·s at 25° C., and mostpreferably from 10 and 500 mPa·s at 25° C. According to one embodiment,the Brookfield viscosity is measured at 100 rpm. Preferably, the milk oflime obtained in step iii) has a Brookfield viscosity from 1 to 1 000mPa·s at 25° C., more preferably from 5 and 800 mPa·s at 25° C., andmost preferably from 10 and 500 mPa·s at 25° C., at solids content of atleast 8 wt.-%, preferably from 10 to 66 wt.-%, more preferably from 12to 66 wt.-%, even more preferably from 15 to 55 wt.-%, and mostpreferably from 17 to 45 wt.-%, such as from 20 to 38 wt.-%, based onthe total weight of the milk of lime.

It is within the confines of the present invention that additional watermay be introduced during the slaking reaction in order to control and/ormaintain and/or achieve the desired solids content or Brookfieldviscosity of the milk of lime.

Process step iii) can be carried out in form of a batch process, asemi-continuous or a continuous process. FIG. 1 shows an example of acontinuous process step iii). The at least on copolymer (2), theoptional slaking additive (3), water (4), and a calcium oxide containingmaterial (5) are fed into a slaker (1). The reaction heat (6) resultingfrom the exothermic slaking reaction is dissipated and the obtained milkof lime is discharged (7) to the next process stage, for example, thecarbonation stage or a screening stage.

Process Step iv): Carbonating the Milk of Lime

According to step iv) of the process of the present invention, the milkof lime obtained from step iii) is carbonated to form an aqueoussuspension of precipitated calcium carbonate.

The carbonation is carried out by means and under conditions well-knownby the person skilled in the art. The introduction of carbon dioxideinto the milk of lime quickly increases the carbonate ion (CO₃ ²⁻)concentration and calcium carbonate is formed. Particularly, thecarbonation reaction can be readily controlled considering the reactionsinvolved in the carbonation process. Carbon dioxide dissolves accordingto its partial pressure forming carbonate ions via the formation ofcarbonic acid (H₂CO₃), and hydrogen carbonate ions (HCO₃ ⁻) beingunstable in the alkaline solution. Upon continued dissolution of carbondioxide, hydroxide ions are consumed and the concentration of carbonateions increases until the concentration of dissolved calcium carbonateexceeds the solubility product and solid calcium carbonate precipitates.

According to one embodiment of the present invention, in step iv) thecarbonation is carried out by feeding pure gaseous carbon dioxide ortechnical gases containing at least 10 vol.-% of carbon dioxide into themilk of lime.

The progress of the carbonation reaction can be readily observed bymeasuring the conductivity density, turbidity and/or pH. In thisrespect, the pH of the milk of lime before addition of carbon dioxidewill be more than 10, usually between 11 and 12.5, and will constantlydecrease until a pH of about 7 is reached. At this point the reactioncan be stopped.

Conductivity slowly decreases during the carbonation reaction andrapidly decreases to low levels, when the precipitation is completed.The progress of the carbonation may be monitored by measuring the pHand/or the conductivity of the reaction mixture.

According to one embodiment of the present invention, the temperature ofthe milk of lime obtained from step iii), which is used in step iv) isadjusted to be in the range from 20° C. to 65° C., and preferably from30° C. to 55° C. It will be apparent to the skilled person that theinitial temperature of the milk of lime, is not necessarily the same oneas the temperature of the mixture prepared in step iv) due to theexothermic carbonation reaction and/or due to the mixing of substanceshaving different temperatures.

According to one embodiment of the present invention, step iv) iscarried out at a temperature from 5 to 95° C., preferably from 30 to 70°C., and more preferably from 40 to 60° C.

Process step iv) can be carried out in form of a batch process, asemi-continuous or a continuous process. According to one embodiment,the process of the present invention involving the process steps i) toiv) is carried out in form of a batch process, a semi-continuous or acontinuous process.

According to one embodiment of the present invention, the process of thepresent invention does not comprise a step of up-concentrating theaqueous suspension of precipitated calcium carbonate obtained by stepsi) to iv) of the inventive process. Additionally or alternatively, theprocess of the present invention does not comprise a step of separatingthe liquid phase from the solids content in the suspension obtained instep iii), i.e. there is no step of separating carried out between stepsiii) and iv) of the inventive process.

As already mentioned above, the inventors surprisingly found that theaddition of at least one copolymer as defined above before or during theslaking step of a process for producing PCC can allow the preparation ofa PCC suspension with a high solids content. It is also believed thatthe omission of a concentration step improves the quality of theproduced PCC particles, since surface damages of the particles, whichcan occur during the concentration step, are avoided. It was also foundthat said PCC suspension can be further up-concentrated to a solidscontents of about 70 wt.-% at acceptable viscosities, for example, toBrookfield viscosities of less than or equal to 1 600 mPa-s at 25° C.and 100 rpm. Typically, this cannot be done with PCC suspensions thatare obtained by conventional PCC production processes including anup-concentrating step because the viscosity of said suspension wouldrise to a non-pumpable range.

According to one embodiment of the present invention, the obtainedprecipitated calcium carbonate has a weight median particle size d₅₀from 0.1 to 100 μm, preferably from 0.25 to 50 μm, more preferably from0.3 to 5 μm, and most preferably from 0.4 to 3.0 μm.

The precipitated calcium carbonate may have aragonitic, calcitic, orvateritic crystal structure, or mixtures thereof. It is a furtheradvantage of the present invention that the crystal structure andmorphology of the precipitated calcium carbonate can be controlled, e.g.by addition of seed crystals or other structure modifying chemicals.According to a preferred embodiment, the precipitated calcium carbonateobtained by the inventive process has a clustered scalenohedral crystalstructure.

The BET specific surface area of the precipitated calcium carbonateobtained by the process according to the present invention may be from 1to 100 m²/g, preferably from 2 to 70 m²/g, more preferably from 3 to 50m²/g, especially from 4 to 30 m²/g, measured using nitrogen and the BETmethod according to ISO 9277. The BET specific surface area of theprecipitated calcium carbonate obtained by the process of the presentinvention may be controlled by the use of additives, e.g. surface activeagents, shearing during the precipitation step or thereafter at highmechanical shearing rates not only leading to a low particle size, butalso to a high BET specific surface area.

According to one embodiment of the present invention, the suspension ofprecipitated calcium carbonate obtained in step iv) has preferably asolids content of at least 15 wt.-%, preferably from 15 to 70 wt.-%,more preferably from 19 to 60 wt.-%, even more preferably from 21 to 50wt.-% and most preferably from 24 to 42 wt.-%, based on the total weightof the suspension.

According to one embodiment of the present invention, the suspension ofPCC obtained in step iv) has a Brookfield viscosity of less than orequal to 3 000 mPa·s at 25° C. For example, the suspension of PCCobtained in step iv) has a Brookfield viscosity of less than or equal to3 000 mPa·s at 25° C., at solids content of at least 15 wt.-%,preferably from 15 to 70 wt.-%, more preferably from 19 to 60 wt.-%,even more preferably from 21 to 50 wt.-% and most preferably from 24 to42 wt.-%, based on the total weight of the suspension.

Preferably, the suspension of PCC obtained in step iv) has a Brookfieldviscosity of less than or equal to 2 500 mPa·s at 25° C., morepreferably less than or equal to 2 000 mPa·s at 25° C., and mostpreferably less than or equal to 600 mPa·s at 25° C.

The Brookfield viscosity is measured at 100 rpm. For example, thesuspension of PCC obtained in step iv) has a Brookfield viscosity ofless than or equal to 2 500 mPa·s at 25° C., more preferably less thanor equal to 2 000 mPa·s at 25° C., and most preferably less than orequal to 600 mPa·s at 25° C., at solids content of at least 15 wt.-%,preferably from 15 to 70 wt.-%, more preferably from 19 to 60 wt.-%,even more preferably from 21 to 50 wt.-% and most preferably from 24 to42 wt.-%, based on the total weight of the suspension.

Optional Process Steps

In one embodiment, the process further comprises step v) of adding atleast one slaking additive to process step iii).

According to one embodiment of the present invention, the at least oneslaking additive is selected from the group consisting of organic acids,organic acid salts, sugar alcohols, monosaccharides, disaccharides,polysaccharides, gluconates, phosphonates, lignosulphonates, andmixtures thereof.

For example, the at least one slaking additive is selected from thegroup consisting of sodium citrate, potassium citrate, calcium citrate,magnesium citrate, monosaccharides, disaccharides, polysaccharides,sucrose, sugar alcohols, meritol, citric acid, sorbitol, sodium salt ofdiethylene triamine pentaacetic acid, gluconates, phosphonates, sodiumtartrate, sodium lignosulphonate, calcium lignosulphonate, and mixturesthereof. According to a preferred embodiment, the at least one slakingadditive is sodium citrate and/or saccharose.

According to one embodiment of the present invention, the at least oneslaking additive consists of one type of slaking additive only.Alternatively, the at least one slaking additive can consist of amixture of two or more types of slaking additives.

The at least one slaking additive may be provided in an amount from 0.01to 2.0 wt.-%, based on the total amount of calcium oxide containingmaterial, preferably in an amount from 0.05 to 1.0 wt.-%, morepreferably from 0.06 to 0.8 wt.-%, and most preferably from 0.07 to 0.5wt.-%.

By adding a slaking additive, the size of the PCC particles and theircrystal morphology can be controlled without affecting the viscosity ofthe final aqueous suspension.

If the process of the present invention comprises a step of adding atleast one slaking additive to process step iii), the process step iii)preferably comprises the steps of:

-   -   a1) mixing the at least one copolymer of step ii) and the at        least one slaking additive with water, and    -   a2) adding the calcium oxide containing material of step i) to        the mixture of step a1).

Alternatively, process step iii) comprises the steps of:

-   -   b1) mixing the calcium oxide containing material of step i), the        at least one copolymer of step ii), and the at least one slaking        additive, and    -   b2) adding water to the mixture of step b1).

Alternatively, in process step iii) the calcium oxide containingmaterial of step i), the at least one copolymer of step ii), the atleast one slaking additive, and water are mixed simultaneously.

According to still another embodiment of the present invention, the atleast one slaking additive is added before or after step iii) of theinventive process.

It is appreciated that the Brookfield viscosity of the suspension of PCCobtained in step iv) may vary if at least one slaking additive is addedto process step iii).

For example, if at least one slaking additive is added to process stepiii), the suspension of PCC obtained in step iv) preferably has aBrookfield viscosity of less than or equal to 2 000 mPa·s at 25° C.,e.g. less than or equal to 1 500 mPa·s at 25° C. For example, thesuspension of PCC obtained in step iv) has a Brookfield viscosity in therange from 10 to 1 500 mPa·s at 25° C. such as from 100 to 6 mPa·s at25° C. Preferably, if at least one slaking additive is added to processstep iii), the suspension of PCC obtained in step iv) has a Brookfieldviscosity of less than or equal to 2 000 mPa·s at 25° C., morepreferably less than or equal to 1 500 mPa·s at 25° C., even morepreferably in the range from 10 to 1 500 mPa·s at 25° C. and mostpreferably from 100 to 600 mPa·s at 25° C., at solids content of atleast 15 wt.-%, preferably from 15 to 70 wt.-%, more preferably from 19to 60 wt.-%, even more preferably from 21 to 50 wt.-% and mostpreferably from 24 to 42 wt.-%, based on the total weight of thesuspension.

If process step iii) is carried out in the absence of at least oneslaking additive, i.e. no slaking additive is added to process stepiii), the suspension of PCC obtained in step iv) preferably has aBrookfield viscosity of less than or equal to 3 000 mPa·s at 25° C.,more preferably less than or equal to 2 500 mPa·s at 25° C., and mostpreferably less than or equal to 2 000 mPa·s at 25° C. Preferably, ifprocess step iii) is carried out in the absence of at least one slakingadditive, the suspension of PCC obtained in step iv) preferably has aBrookfield viscosity of less than or equal to 3 000 mPa·s at 25° C.,more preferably less than or equal to 2 500 mPa·s at 25° C., and mostpreferably less than or equal to 2 000 mPa·s at 25° C., e.g. in therange from 1 000 to 2 000 mPa·s at 25° C. or from 1 500 to 2 000 mPa·sat 25° C., at solids content of at least 15 wt.-%, preferably from 15 to70 wt.-%, more preferably from 19 to 60 wt.-%, even more preferably from21 to 50 wt.-% and most preferably from 24 to 42 wt.-%, based on thetotal weight of the suspension.

In one embodiment of the present application, the milk of lime may bescreened in order to remove oversize particles. A suitable screen caninclude, for example, a screen having a sieve size from 700 to 100 μm,for example, about 100 or about 300 μm. According to one embodiment ofthe present invention, the milk of lime is screened after step iii) andbefore step iv), preferably with a screen having a sieve size from 100to 300 μm. It is to be noted that such a screening step is to bedistinguished from a separating step as only particles of a specificsize are removed. In contrast thereto, a separating step essentiallycompletely removes the solids from an aqueous suspension.

It is possible to separate the precipitated calcium carbonate from theaqueous suspension obtained in step iv). In one embodiment, the processaccording to the present invention comprising the steps i) to iv), andoptionally step v), thus further comprises step vi) of separating theprecipitated calcium carbonate from the aqueous suspension obtained instep iv).

For the purpose of the present invention, the expression “separating”means that the PCC is removed or isolated from the aqueous suspensionobtained from step iv) of the inventive process. The precipitatedcalcium carbonate obtained from step iv) may be separated from themother liquor by any conventional means of separation known to theskilled person. According to one embodiment of the present invention, inprocess step vi) the PCC is separated mechanically and/or thermally.Examples for mechanical separation processes are filtration, e.g. bymeans of a drum filter or filter press, nanofiltration, orcentrifugation. An example for a thermal separation process is aconcentration process by the application of heat, for example, in anevaporator. According to a preferred embodiment, in process step vi) thePCC is separated mechanically, preferably by filtration and/orcentrifugation.

It is also preferred that the mother liquor obtained after precipitationand/or any one of the reactants may be recycled into the process.

The obtained PCC may be further processed, e.g., may be deagglomeratedor subjected to a dry grinding step. Otherwise, it may also be wetground in form of a suspension. If the PCC is subjected to dewatering,dispersion and/or grinding steps, these steps may be accomplished byprocedures known in the art. Wet grinding may be carried out in theabsence of a grinding aid or in the presence of a grinding aid. One ormore grinding agents can be included, such as, e.g., sodiumpolyacrylate, a salt of polyacrylate acid, and/or a salt of a copolymerof acrylic acid. Dispersants also can be included to prepare dispersionsif desired.

In one embodiment, the separated precipitated calcium carbonate obtainedfrom step vi) is dried in drying step vii). Thus, a process forproducing a precipitated calcium carbonate is provided comprising thesteps of:

-   -   i) providing a calcium oxide containing material,    -   ii) providing at least one copolymer of the following formula        (I)

-   -   wherein x, y and z are present in blocks, alternating or        randomly; x is >0 and at least one of y or z is >0 and the sum        of x+y+z is ≤150; R₁ represents hydrogen or a sulphonic        functional group; R₂ represents a heteroatom, optionally        substituted with an alkyl group, an alkenyl group, an heteroaryl        group and/or a polyalkoxylated group; R₃ and R₄ are        independently from each other a hydroxyl group, (O⁻M⁺) with M⁺        being a monovalent, divalent or trivalent cation, an O-alkyl        group comprising from 1 to 20 carbon atoms, an N-alkyl group        comprising from 1 to 20 carbon atoms and/or a polyalkoxylated        group    -   iii) preparing a milk of lime by mixing water, the calcium oxide        containing material of step i), and the at least one copolymer        of step ii) to obtain a milk of lime, wherein the calcium oxide        containing material and the water are mixed in a weight ratio        from 1:1 to 1:12,    -   iv) carbonating the milk of lime obtained in step iii) to form        an aqueous suspension of precipitated calcium carbonate,    -   v) optionally adding at least one slaking additive to process        step iii),    -   vi) separating the precipitated calcium carbonate from the        aqueous suspension obtained in step iv), and    -   vii) drying the precipitated calcium carbonate obtained in step        vi).

In general, the drying step vii) may take place using any suitabledrying equipment and can, for example, include thermal drying and/ordrying at reduced pressure using equipment such as an evaporator, aflash drier, an oven, a spray drier and/or drying in a vacuum chamber.

According to one embodiment, drying step vii) is a spray drying step,preferably said spray drying step is carried out at a lower temperatureranging from 90° C. to 130° C. and preferably from 100° C. to 120° C. Bymeans of drying step vii), a dried precipitated calcium carbonate isobtained having a low total moisture content which is less than or equalto 1.0 wt.-%, based on the total weight of the dried precipitatedcalcium carbonate.

According to another embodiment, the dried PCC of step vii) has a totalmoisture content of less than or equal to 0.5 wt.-% and preferably lessthan or equal to 0.2 wt.-%, based on the total weight of the driedprecipitated calcium carbonate. According to still another embodiment,the dried PCC of step vii) has a total moisture content of between 0.01and 0.15 wt.-%, preferably between 0.02 and 0.10 wt.-%, and morepreferably between 0.03 and 0.07 wt.-%, based on the total weight of thedried precipitated calcium carbonate.

The precipitated calcium carbonate obtained by the inventive process canbe post-treated, for example, during and/or after a drying step with anadditional component.

According to one embodiment the process of the present invention furthercomprises a step viii) of contacting at least a part of the surface ofthe obtained precipitated calcium carbonate with at least onehydrophobising agent after step iv) and/or after step vi), if present,and/or during and/or after step vii), if present. Preferably, at least apart of the surface of the obtained precipitated calcium carbonate maybe contacted with at least one hydrophobising agent during and/or afterstep vii).

Suitable hydrophobising agents are, for example, aliphatic carboxylicacid having a total amount of carbon atoms from C₄ to C₂₄ and/orreaction products thereof, a mono-substituted succinic anhydrideconsisting of succinic anhydride mono-substituted with a group selectedfrom a linear, branched, aliphatic and cyclic group having a totalamount of carbon atoms from at least C₂ to C₃₀ in the substituent and/orreaction products thereof, a phosphoric acid ester blend of one or morephosphoric acid mono-ester and/or reaction products thereof and one ormore phosphoric acid di-ester and/or reaction products thereof,polyhydrogensiloxane and reaction products thereof, an inert siliconeoil, preferably polydimethylsiloxane, an aliphatic aldehyde having from6 to 14 carbon atoms and/or reaction products thereof, and mixturesthereof. Suitable hydrophobising agents and methods for preparingsurface-treated filler products thereof are, for example, described inEP 2 159 258 A1, EP 2 390 285 A1, EP 2 390 280 A1, WO 2014/060286 A1, EO2014/128087 A1, EP 2 722 368 A1 and EP 2 770 017 A1 which are thusincorporated herewith by references.

In one embodiment, the hydrophobising agent is an aliphatic carboxylicacid having a total amount of carbon atoms from C₄ to C₂₄ and/orreaction products thereof. The term “reaction products” of the aliphaticcarboxylic acid in the meaning of the present invention refers toproducts obtained by contacting the modified mineral-based filler withthe at least one aliphatic carboxylic acid. Said reaction products areformed between at least a part of the at least one aliphatic carboxylicacid and reactive molecules located at the surface of the alkaline earthmetal carbonate-comprising material particles.

The aliphatic carboxylic acid in the meaning of the present inventionmay be selected from one or more straight chain, branched chain,saturated, unsaturated and/or alicyclic carboxylic acids. Preferably,the aliphatic carboxylic acid is a monocarboxylic acid, i.e. thealiphatic carboxylic acid is characterized in that a single carboxylgroup is present. Said carboxyl group is placed at the end of the carbonskeleton.

In one embodiment of the present invention, the aliphatic carboxylicacid is selected from saturated unbranched carboxylic acids, that is tosay the aliphatic carboxylic acid is preferably selected from the groupof carboxylic acids consisting of pentanoic acid, hexanoic acid,heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoicacid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid,palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid,arachidic acid, heneicosylic acid, behenic acid, tricosylic acid,lignoceric acid and mixtures thereof.

In another embodiment of the present invention, the aliphatic carboxylicacid is selected from the group consisting of octanoic acid, decanoicacid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidicacid and mixtures thereof. Preferably, the aliphatic carboxylic acid isselected from the group consisting of myristic acid, palmitic acid,stearic acid and mixtures thereof. For example, the aliphatic carboxylicacid is stearic acid.

Additionally or alternatively, the hydrophobising agent can be at leastone mono-substituted succinic acid and/or salty reaction product(s)and/or at least one phosphoric acid ester blend of one or morephosphoric acid mono-ester and/or reaction products thereof and one ormore phosphoric acid di-ester and/or reaction products thereof. Methodsfor treating a calcium carbonate-comprising material with thesehydrophobising agents are described, for example, in EP 2 722 368 A1 andEP 2 770 017 A1 which are thus incorporated herewith by references.

The term “succinic anhydride”, also called dihydro-2,5-furandione,succinic acid anhydride or succinyl oxide, has the molecular formulaC₄H₄O₃ and is the acid anhydride of succinic acid. The term“mono-substituted succinic anhydride” in the meaning of the presentinvention refers to a succinic anhydride wherein a hydrogen atom issubstituted by another substituent.

The term “reaction products of at least one mono-substituted succinicanhydride” in the meaning of the present invention refers to productsobtained by contacting a alkaline earth metal carbonate-comprisingmaterial with one or more mono-substituted succinic anhydride(s). Saidsalty reaction products are formed between the mono-substituted succinicacid which is formed from the applied mono-substituted succinicanhydride and reactive molecules located at the surface of the alkalineearth metal carbonate-comprising material.

The term “phosphoric acid mono-ester” in the meaning of the presentinvention refers to an o-phosphoric acid molecule mono-esterified withone alcohol molecule selected from unsaturated or saturated, branched orlinear, aliphatic or aromatic alcohols having a total amount of carbonatoms from C₆ to C₃₀, preferably from C₈ to C₂₂, more preferably from C₈to C₂₀, and most preferably from C₈ to C₁₈ in the alcohol substituent.The term “phosphoric acid di-ester” in the meaning of the presentinvention refers to an o-phosphoric acid molecule di-esterified with twoalcohol molecules selected from the same or different, unsaturated orsaturated, branched or linear, aliphatic or aromatic alcohols having atotal amount of carbon atoms from C₆ to C₃₀, preferably from C₈ to C₂₂,more preferably from C₈ to C₂₀, and most preferably from C₈ to C₁₈ inthe alcohol substituent.

The term “salty reaction products of a phosphoric acid ester or blend ofone or more phosphoric acid mono-esters and/or one or more phosphoricacid di-esters” in the meaning of the present invention refers toproducts obtained by contacting an alkaline earth metalcarbonate-comprising material with one or more phosphoric acidmono-ester and one or more phosphoric acid di-ester and optionallyphosphoric acid. Said salty reaction products are formed between theapplied one or more phosphoric acid mono-ester and one or morephosphoric acid di-ester and optionally phosphoric acid and reactivemolecules located at the surface of the alkaline earth metalcarbonate-comprising material.

According to one embodiment, the at least one hydrophobising agent isselected from the group consisting of an aliphatic carboxylic acidhaving a total amount of carbon atoms from C₄ to C₂₄ and/or reactionproducts thereof, a mono-substituted succinic anhydride consisting ofsuccinic anhydride mono-substituted with a group selected from a linear,branched, aliphatic and cyclic group having a total amount of carbonatoms from at least C₂ to C₃₀ in the substituent and/or reactionproducts thereof, a phosphoric acid ester blend of one or morephosphoric acid mono-ester and/or reaction products thereof and one ormore phosphoric acid di-ester and/or reaction products thereof,polyhydrogensiloxane and reaction products thereof, an inert siliconeoil, preferably polydimethylsiloxane, an aliphatic aldehyde having from6 to 14 carbon atoms and/or reaction products thereof, and mixturesthereof.

According to a preferred embodiment, the at least one hydrophobisingagent is a mono-substituted succinic anhydride consisting of succinicanhydride mono-substituted with a group selected from a linear,branched, aliphatic and cyclic group having a total amount of carbonatoms from at least C₂ to C₃₀ in the substituent and/or a reactionproduct thereof

Products and their Use

According to the present invention, an aqueous suspension ofprecipitated calcium carbonate is provided, which is obtainable by aprocess comprising the steps of:

-   -   i) providing a calcium oxide containing material,    -   ii) providing at least one copolymer of the following formula        (I)

-   -   wherein x, y and z are present in blocks, alternating or        randomly; x is >0 and at least one of y or z is >0 and the sum        of x+y+z is ≤150; R₁ represents hydrogen or a sulphonic        functional group; R₂ represents a heteroatom, optionally        substituted with an alkyl group, an alkenyl group, an heteroaryl        group and/or a polyalkoxylated group; R₃ and R₄ are        independently from each other a hydroxyl group, (O⁻M⁺) with M⁺        being a monovalent, divalent or trivalent cation, an O-alkyl        group comprising from 1 to 20 carbon atoms, an N-alkyl group        comprising from 1 to 20 carbon atoms and/or a polyalkoxylated        group,    -   iii) preparing a milk of lime by mixing water, the calcium oxide        containing material of step i), and the at least one copolymer        of step ii) to obtain a milk of lime, wherein the calcium oxide        containing material and the water are mixed in a weight ratio        from 1:1 to 1:12, and    -   iv) carbonating the milk of lime obtained from step iii) to form        an aqueous suspension of precipitated calcium carbonate, and    -   v) optionally, adding at least one slaking additive to process        step iii).

According to a further aspect of the present invention, a precipitatedcalcium carbonate is provided, which is obtainable by a processcomprising the steps of:

-   -   i) providing a calcium oxide containing material,    -   ii) providing at least one copolymer of the following formula        (I)

-   -   wherein x, y and z are present in blocks, alternating or        randomly; x is >0 and at least one of y or z is >0 and the sum        of x+y+z is ≤150; R₁ represents hydrogen or a sulphonic        functional group; R₂ represents a heteroatom, optionally        substituted with an alkyl group, an alkenyl group, an heteroaryl        group and/or a polyalkoxylated group; R₃ and R₄ are        independently from each other a hydroxyl group, (O⁻M⁺) with M⁺        being a monovalent, divalent or trivalent cation, an O-alkyl        group comprising from 1 to 20 carbon atoms, an N-alkyl group        comprising from 1 to 20 carbon atoms and/or a polyalkoxylated        group,    -   iii) preparing a milk of lime by mixing water, the calcium oxide        containing material of step i), and the at least one copolymer        of step ii) to obtain a milk of lime, wherein the calcium oxide        containing material and the water are mixed in a weight ratio        from 1:1 to 1:12,    -   iv) carbonating the milk of lime obtained from step iii) to form        an aqueous suspension of precipitated calcium carbonate,    -   v) optionally, adding at least one slaking additive to process        step iii), and    -   vi) separating the precipitated calcium carbonate from the        aqueous suspension obtained from step iv).

Optionally, the obtained precipitated calcium carbonate can comprise ahydrophobising agent, which covers at least partially the surface of theprecipitated calcium carbonate.

The PCC suspension and/or PCC obtained by the process of the presentinvention may be used in various materials. According to one embodimentof the present invention, the aqueous suspension of precipitated calciumcarbonate according to the present invention is used in aqueousformulations, e.g. in a coating formulation, a paper coatingformulation, a pharmaceutical formulation, an agricultural formulation,a cosmetic formulation or an oral care formulation. According to anotherembodiment of the present invention, the precipitated calcium carbonateaccording to the present invention is used in paper, a paper product, anink, a paint, a coating, a plastic, a polymer composition, an adhesive,a building product, a foodstuff, an agricultural product, a cosmeticproduct or a pharmaceutical product.

According to one aspect of the present invention, a product comprisingthe aqueous suspension of precipitated calcium carbonate according tothe present invention is thus provided. According to a preferredembodiment, the product is an aqueous formulation, and more preferablyis a coating formulation, a paper coating formulation, a pharmaceuticalformulation, an agricultural formulation, a cosmetic formulation or anoral care formulation.

According to another aspect of the present invention, a productcomprising the precipitated calcium carbonate according to the presentinvention is provided. According to a preferred embodiment, the productis a paper, a paper product, an ink, a paint, a coating, a plastic, apolymer composition, an adhesive, a building product, a foodstuff, anagricultural product, a cosmetic product or a pharmaceutical product.

According to still a further aspect of the present invention, a driedprecipitated calcium carbonate is provided, which is obtainable by aprocess comprising the steps of:

-   -   i) providing a calcium oxide containing material,    -   ii) providing at least one copolymer of the following formula        (I)

-   -   wherein x, y and z are present in blocks, alternating or        randomly; x is >0 and at least one of y or z is >0 and the sum        of x+y+z is ≤150; R₁ represents hydrogen or a sulphonic        functional group; R₂ represents a heteroatom, optionally        substituted with an alkyl group, an alkenyl group, an heteroaryl        group and/or a polyalkoxylated group; R₃ and R₄ are        independently from each other a hydroxyl group, (O⁻M⁺) with M⁺        being a monovalent, divalent or trivalent cation, an O-alkyl        group comprising from 1 to 20 carbon atoms, an N-alkyl group        comprising from 1 to 20 carbon atoms and/or a polyalkoxylated        group,    -   iii) preparing a milk of lime by mixing water, the calcium oxide        containing material of step i), and the at least one copolymer        of step ii) to obtain a milk of lime, wherein the calcium oxide        containing material and the water are mixed in a weight ratio        from 1:1 to 1:12,    -   iv) carbonating the milk of lime obtained from step iii) to form        an aqueous suspension of precipitated calcium carbonate,    -   v) optionally, adding at least one slaking additive to process        step iii),    -   vi) separating the precipitated calcium carbonate from the        aqueous suspension obtained from step iv), and    -   vii) drying the separated precipitated calcium carbonate        obtained from step vi).

Optionally, the obtained dried precipitated calcium carbonate cancomprise a hydrophobising agent, which covers at least partially thesurface of the precipitated calcium carbonate.

According to a preferred embodiment, the dried precipitated calciumcarbonate obtainable from process steps i) to vii) is a dried powder ofprecipitated calcium carbonate.

The dried PCC obtainable from process steps i) to vii) may be used inpaper, plastics, polymer compositions, paint, coatings, concrete,cosmetics, pharmaceutics and/or agriculture applications. According to apreferred embodiment, the dried precipitated calcium carbonate is usedin plastics and/or polymer compositions. For example, said PCC may beused in thermoplastic polymers, such as polyvinyl chloride, polyolefins,and polystyrene. Moreover, the dried PCC may also be used in polymercoatings which may be applied on the surface of polymer articles, suchas foils, in order to increase the hydrophobicity (e.g., reflected by anincreased contact angle measured against water) of said surface.

According to one aspect of the present invention, a product comprisingdried precipitated calcium carbonate according to the present invention,preferably a dried powder of said precipitated calcium carbonate, isprovided. According to one embodiment, the product is a paper, a paperproduct, an ink, a paint, a coating, a plastic, a polymer composition,an adhesive, a building product, a foodstuff, an agricultural product, acosmetic product or a pharmaceutical product. According to a preferredembodiment, a product comprising a dried precipitated calcium carbonateis provided, wherein the product is a plastic or a polymer composition.

The scope and interest of the present invention will be betterunderstood based on the following figures and examples which areintended to illustrate certain embodiments of the present invention andare non-limitative.

DESCRIPTION OF THE FIGURE

FIG. 1 is a sketch of a continuous slaking process.

EXAMPLES 1. Measurement Methods

In the following, measurement methods implemented in the examples aredescribed.

Brookfield Viscosity

The Brookfield viscosity of the aqueous suspensions was measured onehour after the production and after one minute of stirring at 25° C.±1°C. at 100 rpm by the use of a Brookfield viscometer type RVT equippedwith an appropriate disc spindle, for example spindle 2 to 5.

pH Value

The pH of a suspension or solution was measured at 25° C. using aMettler Toledo Seven Easy pH meter and a Mettler Toledo InLab® ExpertPro pH electrode. A three point calibration (according to the segmentmethod) of the instrument was first made using commercially availablebuffer solutions having pH values of 4, 7 and 10 at 20° C. (fromSigma-Aldrich Corp., USA). The reported pH values are the endpointvalues detected by the instrument (the endpoint was when the measuredsignal differed by less than 0.1 mV from the average over the last 6seconds).

Particle Size Distribution

The particle size distribution of the prepared PCC particles wasmeasured using a Sedigraph 5120 or 5100 from the company Micromeritics,USA. The method and the instrument are known to the skilled person andare commonly used to determine grain size of fillers and pigments. Themeasurement was carried out in an aqueous solution comprising 0.1 wt.-%Na₄P₂O₇. The samples were dispersed using a high speed stirrer andsupersonics. For the measurement of dispersed samples, no furtherdispersing agents were added.

Solids Content of an Aqueous Suspension

The suspension solids content (also known as “dry weight”) wasdetermined using a Moisture Analyser MJ33 from the companyMettler-Toledo, Switzerland, with the following settings: dryingtemperature of 160° C., automatic switch off if the mass does not changemore than 1 mg over a period of 30 sec, standard drying of 5 to 20 g ofsuspension.

Specific Surface Area (SSA)

The specific surface area was measured via the BET method according toISO 9277 using nitrogen, following conditioning of the sample by heatingat 250° C. for a period of 30 minutes. Prior to such measurements, thesample is filtered within a Buchner funnel, rinsed with deionised waterand dried overnight at 90 to 100° C. in an oven. Subsequently the drycake is ground thoroughly in a mortar and the resulting powder placed ina moisture balance at 130° C. until a constant weight is reached.

Specific Carbonation Time

The monitoring of the conductivity, which slowly decreases during thecarbonation reaction and rapidly decreases to a minimal level, therebyindicating the end of the reaction, was used to assess the time neededto perform the complete precipitation. The specific carbonation time(min/kg Ca(OH)₂) was determined by the following formula:

${{Specific}\mspace{14mu} {carbonation}\mspace{14mu} {time}} = \frac{10^{5} \cdot T_{f}}{M \cdot {SC}_{MoL}}$

wherein:

-   -   T_(f)(min) is the time needed to complete the carbonation of the        milk of lime, as determined by monitoring the conductivity,    -   M (g) is the weight of the milk of lime introduced into the        carbonation reactor, and    -   SC_(MoL) (%) is the weight solids content of the milk of lime.

Charge Measurement—Mütek

The charge measurement was carried out using a Mütek PCD 03 deviceequipped with a Mütek PCD titrator.

About 1 g of the PCC suspension is weighed in the plastic measuring celland is diluted with 20 mL of deionised water. Put the displacementpiston on. While the piston oscillates in the cell, wait until thestreaming current between the two electrodes stabilizes.

The sign of the measured value shown on the display indicates whetherthe charge of the sample is positive (cationic) or negative (anionic).An oppositely charged polyelectrolyte of known charge density is addedto the sample as a titrant (either sodium polyoxyethylene sulphate 0.001N or pDADMAC 0.001 N). The titrant charges neutralize existing chargesof the sample. Titration is discontinued as soon as the point of zerocharge (0 mV) is reached.

Titrant consumption in mL forms the basis for further calculations. Thespecific charge quantity q [Val/g of slurry] is calculated according tothe following formula:

q=(V×c)/m

V: consumed titrant volume [l]c: titrant charge concentration [μVal/l]m: mass of the weighed slurry [g]q: specific charge quantity [μVal/g of slurry]

Zeta Potential

For measuring the Zeta potential, a few drops of the PCC suspensions aredispersed in a sufficient quantity of serum obtained by mechanicalfiltration of the said suspension in order to obtain a colloidalsuspension which is slightly cloudy.

This suspension is introduced into the measuring cell of the ZetasizerNano-ZS from Malvem, which directly displays the value of the Zetapotential of the PCC suspension in mV.

2. Polymers and Slaking Additives

NaCi: Sodium citrate, commercially available from Sigma-Aldrich,Switzerland.

P1: Copolymer of the following formula (III)

-   -   wherein x and z are present alternating; x and z are        independently from each other each an integer in the range from        1 to 149 and the sum of x+z is an integer in the range from 2 to        150; R₁ represents hydrogen; R₃ is (O⁻M⁺) with M⁺ being sodium;        and M⁺ being sodium, and the molar ratio of x to z is about 1:1        (M_(w)=5 000 g/mol; solids content of 30 wt.-%)

P2: polyacrylic acid with the following formula,

-   -   wherein R₁ is H, X is Na, and m=45; the M_(w) being 4 270 g/mol,        and the polydispersity index being 2.3. The molecular weight        M_(w) and the polydispersity index are determined according to        the corresponding method described in EP 14 166 751.9.

3. Examples Example 1

A milk of lime was prepared by mixing under mechanical stirring waterwith dry sodium citrate (NaCi) as slaking additive (if present) andcopolymer P1 (if present) (according to the invention) or polymer P2(comparison) at an initial temperature between 40 and 41° C. (theamounts of slaking additives and copolymer or polymer are indicated inTable 1 below). Subsequently, calcium oxide (quicklime raw material fromGolling, Austria) was added. The obtained mixture was stirred for 25 minand then sieved through a 200 μm screen.

The obtained milk of lime was transferred into a stainless steelreactor, wherein the milk of lime was cooled down to 50° C. Then themilk of lime was carbonated by introducing an air/CO₂ mixture (26 vol-%CO₂ at a rate of 23 L/min). During the carbonation step, the reactionmixture was stirred with a speed of 1 400 rpm. The kinetic of thereaction was monitored by online pH and conductivity measurements.

TABLE 1 Characteristics of produced milks of lime of Example 1 (comp:comparative example; IN: inventive example). Slaking Solids Polymeradditive content amount amount of milk Polymer [wt.-%/wt. Slaking[wt.-%/wt. of lime Sample additive CaO] additive CaO] [wt.-%] 1 (comp)No — NaCi 0.1 25.2 2 (comp) No — NaCi 0.1 16.2 3 (IN) P1 0.15 NaCi 0.126.9 4 (IN) P1 0.15 — — 27.1 5 (comp) P2 0.15 NaCi 0.1 29.5

The characteristics of the prepared milks of lime and aqueous PCCsuspensions are described in Table 2 below.

TABLE 2 Characteristics of the obtained aqueous PCC suspensions ofExample 1 Viscosity Solids of the content Viscosity Mutek milk ofCarbonation of the of the charge lime time PCC PCC Zeta (μVal/g (mPa ·s) (min/kg (wt.- (mPa · s) SSA d₅₀ potential of Sample 100 rpm Ca(OH)₂)%) 100 rpm [m²/g] [μm] (mV) slurry) 1 Viscosity of milk of lime is toohigh Not measured (comp) 2 23 44 20.5 20 4.7 1.6 +5.5 +0.1 (comp) 3 (IN)150 46 35.0 199 4.2 1.5 −18.1 −0.5 4 (IN) 101 51 34.2 1730 4.5 1.7 +3.1+3.4 5 329 47 37.6 940 5.0 1.3 −35.2 −0.9 (comp) (comp: comparativeexample).

The results compiled in Table 2 show that the use of a slaking additivealone leads to a milk of lime (calcium hydroxide suspension) having ahigh Brookfield viscosity (sample 1), and it is not possible to increasethe solids content of the milk of lime without an increase in theviscosity of the suspension (comparison of sample 1 and sample 2).

By contrast, inventive sample 3 confirms that the viscosity of theobtained milk of lime and PCC suspension is totally compatible with theintended use of the PCC so obtained that is to say suspensions of PCChaving a Brookfield viscosity of less than or equal to 1 500 mPa·s at25° C. Additionally, the kinetic of carbonation and the crystallographicstructure of the prepared PCC (results not shown) is similar to the oneobtained with a process involving the use of an anionic polymer (P2:polyacrylic acid where 100 mole-% of the carboxylic groups have beenneutralized by sodium ions, the M_(w) being 4270 g/mol, and thepolydispersity index being 2.3; sample being outside of the invention).

1. A process for producing an aqueous suspension of precipitated calciumcarbonate comprising the steps of: i) providing a calcium oxidecontaining material; ii) providing at least one copolymer of thefollowing formula (I)

wherein x, y and z are present in blocks, alternating or randomly; xis >0 and at least one of y or z is >0 and the sum of x+y+z is ≤150; R₁represents hydrogen or a sulphonic functional group; R₂ represents aheteroatom, optionally substituted with an alkyl group, an alkenylgroup, an heteroaryl group and/or a polyalkoxylated group; R₃ and R₄ areindependently from each other a hydroxyl group, (O⁻M⁺) with M⁺ being amonovalent, divalent or trivalent cation, an O-alkyl group comprisingfrom 1 to 20 carbon atoms, an N-alkyl group comprising from 1 to 20carbon atoms and/or a polyalkoxylated group; iii) preparing a milk oflime by mixing water, the calcium oxide containing material of step i),and the at least one copolymer of step ii) to obtain a milk of lime,wherein the calcium oxide containing material and the water are mixed ina weight ratio from 1:1 to 1:12; and iv) carbonating the milk of limeobtained in step iii) to form an aqueous suspension of precipitatedcalcium carbonate.
 2. The process of claim 1, wherein step iii)comprises the steps of: a1) mixing the at least one copolymer of stepii) with water, and a2) adding the calcium oxide containing material ofstep i) to the mixture of step a1); or b1) mixing the calcium oxidecontaining material of step i), and the at least one copolymer of stepii), and b2) adding water to the mixture of step b1); or c) mixing thecalcium oxide containing material of step i), the at least one copolymerof step ii) and water simultaneously.
 3. The process of claim 1, whereinthe process further comprises step v) of adding at least one slakingadditive to process step iii), preferably the at least one slakingadditive is selected from the group consisting of organic acids, organicacid salts, sugar alcohols, monosaccharides, disaccharides,polysaccharides, gluconates, phosphonates, lignosulphonates, andmixtures thereof.
 4. The process of claim 1, wherein the milk of limeobtained in step iii) has a Brookfield viscosity from 1 to 1 000 mPa·sat 25° C., more preferably from 5 to 800 mPa·s at 25° C., and mostpreferably from 10 to 500 mPa·s at 25° C.; and/or the suspension of PCCobtained in step iv) has a Brookfield viscosity of less than or equal to3 000 mPa·s at 25° C., more preferably less than or equal to 2 500 mPa·sat 25° C., and most preferably less than or equal to 600 mPa·s at 25° C.5. The process of claim 1, wherein the suspension of PCC obtained instep iv) has solids content of at least 15 wt.-%, preferably from 15 to70 wt.-%, more preferably from 19 to 60 wt.-%, even more preferably from21 to 50 wt.-% and most preferably from 24 to 42 wt.-%, based on thetotal weight of the suspension.
 6. The process of claim 1, wherein thetemperature of the water, which is used in mixing step iii), is adjustedto be in the range from more than 0° C. and less than 100° C.,preferably from 1° C. to 85° C., more preferably from 2° C. to 70° C.,even more preferably from 30° C. to 65° C., and most preferably from 35to 55° C.; and/or the temperature of the milk of lime obtained in stepiii), which is employed in step iv), is adjusted to be in the range from20° C. to 65° C., and preferably from 30° C. to 55° C.
 7. The process ofclaim 1, wherein the at least one copolymer of step ii) is a compound ofthe following formula (II)

wherein x and y are present in blocks, alternating or randomly; x and yare >0 and the sum of x+y is ≤150; R₁ represents hydrogen or a sulphonicfunctional group; R₂ represents a heteroatom, optionally substitutedwith an alkyl group, an alkenyl group, an heteroaryl group and/or apolyalkoxylated group.
 8. The process of claim 1, wherein the at leastone copolymer of step ii) is a compound of the following formula (III)

wherein x and z are present in blocks, alternating or randomly; x and zare >0 and the sum of x+z is ≤150; R₁ represents hydrogen or a sulphonicfunctional group; R₃ is a hydroxyl group, (O⁻M⁺) with M⁺ being amonovalent, divalent or trivalent cation, an O-alkyl group comprisingfrom 1 to 20 carbon atoms, an N-alkyl group comprising from 1 to 20carbon atoms and/or a polyalkoxylated group; and M⁺ being a monovalent,divalent or trivalent cation.
 9. The process of claim 1, wherein themolar ratio of x to y and/or z in the at least one copolymer of step ii)[x:y and/or z] is from 10:1 to 1:2, preferably from 5:1 to 1:2 and mostpreferably about 1:1, 2:1 or 3:1.
 10. The process of claim 1, whereinthe at least one copolymer of step ii) has a molecular weight M_(w) inthe range from 500 to 100 000 g/mol, preferably from 1 000 to 50 000g/mol, more preferably from 2 000 to 20 000 g/mol and most preferablyfrom 2 500 to 10 000 g/mol; and/or, provided in a water solution, has aBrookfield viscosity of less than or equal to 5 000 mPa·s at 25° C.,more preferably less than or equal to 2 000 mPa·s at 25° C., and mostpreferably less than or equal to 1 500 mPa·s at 25° C.
 11. The processof claim 1, wherein the process further comprises step vi) of separatingthe precipitated calcium carbonate from the aqueous suspension obtainedin step iv), and optionally step vii) of drying the separatedprecipitated calcium carbonate obtained in step vi).
 12. The process ofclaim 1, wherein the process further comprises a step viii) ofcontacting at least a part of the surface of the obtained precipitatedcalcium carbonate with at least one hydrophobising agent after step iv)and/or after step vi), if present, and/or during and/or after step vii),if present, preferably the at least one hydrophobising agent is selectedfrom the group consisting of an aliphatic carboxylic acid having a totalamount of carbon atoms from C₄ to C₂₄ and/or reaction products thereof,a mono-substituted succinic anhydride consisting of succinic anhydridemono-substituted with a group selected from a linear, branched,aliphatic and cyclic group having a total amount of carbon atoms from atleast C₂ to C₃₀ in the substituent and/or reaction products thereof, aphosphoric acid ester blend of one or more phosphoric acid mono-esterand/or reaction products thereof and one or more phosphoric aciddi-ester and/or reaction products thereof, polyhydrogensiloxane andreaction products thereof, an inert silicone oil, preferablypolydimethylsiloxane, an aliphatic aldehyde having from 6 to 14 carbonatoms and/or reaction products thereof, and mixtures thereof.
 13. Anaqueous suspension of precipitated calcium carbonate obtainable by aprocess according to claim
 1. 14. A product comprising an aqueoussuspension of precipitated calcium carbonate according to claim 13,preferably the product is an aqueous formulation, and more preferably isa coating formulation, a paper coating formulation, a pharmaceuticalformulation, an agricultural formulation, a cosmetic formulation or anoral care formulation.
 15. Precipitated calcium carbonate obtainable bya process according to claim
 11. 16. A product comprising precipitatedcalcium carbonate according to claim 15, preferably the product is apaper, a paper product, an ink, a paint, a coating, a plastic, a polymercomposition, an adhesive, a building product, a foodstuff, anagricultural product, a cosmetic product or a pharmaceutical product,and more preferably the precipitated calcium carbonate is a driedprecipitated calcium carbonate and the product is a plastic or a polymercomposition.
 17. (canceled)